Note: Descriptions are shown in the official language in which they were submitted.
CA 02564692 2006-10-25
1
METHOD FOR PRODUCING COATED SUBSTRATES
The invention relates to a process for the production of laminated substrates.
The
invention furthermore relates to aminoplast resin sheets or films, and the use
of a
modified decorative paper for the production of aminoplast resin sheets or
films for 3D
lamination.
Usually, thern-ioplastic slieets are used for lamination with three-
dimensionally
structured surfaces (3D lamination), for example for the lamination of wood-
base
materials in the furniture industry. The important advantage of these
thermoplastic
sheets is the resilience thereof, but the high costs of production, due inter
alia to the
additional use of adhesives, are disadvantageous.
The use of the self-adhesive economical melamine resins, which are used, for
example, in the furniture industry for finishing smooth surfaces, is also
desirable for the
lamination of three-dimensionally structured surfaces. The melamine resins are
furthermore distinguished by high gloss and good printability.
However, pure melamine resins are too brittle for this application.
Improved flexibility of the sheets could be achieved according to DE-A 23 09
334 by
means of etherified melamine resins carrying methylol groups. These melamine
resin
sheets are used in particular for the surface finishing of wood-base
materials, such as
hard particle boards and blockboards. In order to achieve the flexibility and
resilience
,?n required for the lamination of, for example, rounded edges, the melamine
resins were
'v further modified, for example by adding guanamine, according to DE-A 44 39
156, or
by adding small amounts of an aqueous synthetic resin dispersion, according to
DE-A 38 37 965. According to DE-A 37 00 344, a combination of aminoplast
resins with
acrylate dispersions results in a certain resilience of the sheets produced,
but a high
proportion of dispersion caused a substantial loss of stretchability and
internal bond
strength, properties which are necessary precisely in the lamination of three-
dimensionally structured surfaces.
The prior German Application with the application number 10301901.4 discloses
for the
first time self-adhesive melamine resin films which can be used directly for
3D
lamination of pieces of furniture. These melamine resins consist of a mixture
of
melamine/formaldehyde condensates, etherified melamine/formaldehyde
condensates
30 and acrylate dispersions. The melamine resin films described are well
suited for the
lamination of three-dimensionally shaped surfaces.
PF 55625 CA 02564692 2006-10-25
2
Improved flexibility of the sheets could furthermore be achieved by modifying
the
decorative paper to be impregnated with the melamine resin. WO 00/53666,
WO 00/53667, WO 00/53668 and VVO 02/38345 describe d ifferent fiber papers for
the
lamination of, for example, bodies having three-dimensional structures. WO
00/53666
discloses for this purpose a carrier which consists of meltable polymers and
cellulose
or regenerated cellulose. Cellulose esters and preferably cellulose acetate
are
described as meltable polymers. WO 00/53667 describes fiber papers with the
use of
carriers based completely or partly on regenerated cellulose. The regeneration
of the
cellulose consists in a conversion into a soluble cellulose derivative with
the use of an
acid, it being possible to convert the derivative into fibers and, if
appropriate, to reduce
the size of the fibers. WO 00/53668 describes carriers comprising fibrous
cellulose
esters, preferably cellulose acetates. WO 02/38345 describes the use of
decorative
paper which contains at least 10% by weight and up to 100% by weight, based on
the
total fiber content, of cotton linters for the lamination of three-
dimensionally structured
surfaces.
In spite of the successes achieved to date, the known sheets or films
comprising the
modified melamine resins and decorative papers are still worthy of
improvement. In
particular, there is still a need to optimize the property of resilience of
the sheets or of
the films. For esthetic reasons and simultaneously for simplifying the
production, the
lamination should be effected only with a single sheet or film in a single
pressing
process. The main feature of such sheets or films is the moldability during
the pressing
process.
It was accordingly the object of the invention to provide an improved process
for the
production of a laminated substrate havina a three-dimensionallv str~ icti
irPri ci irfarP. In
particular, it was intended to provide a process for the production of a
laminated piece
of furniture or wood-base material having a three-dimensionally structured
surface.
Furthermore, it was intended to provide a more flexible melamine resin sheet
or film
which is also suitable for the 3D lamination and in particular for the
complete
surrounding of structures. The laminated surfaces should have no white
fracture, i.e.
background which gleams through, and undesired creases at the compression
points.
A process which is particularly suitable for the production of partly or
completely
laminated substrates having a three-dimensionally structured surface, in which
a
decorative paper which comprises from 5 to 90% by weight, based on the total
fiber
content, of fibers of synthetic polymers is impregnated with a crosslinkable
aminoplast
resin, applied to a substrate and three-dimensionally shaped, was surprisingly
found.
The term "three-dimensional shaping" is to be understood as meaning the
partial or
complete lamination of bodies, structures, reliefs, profiles, embossings and
the like.
These have three-dimensionally structured surfaces, i.e. shapes, forms or
structures
PF 55625 CA 02564692 2006-10-25
3
which extend in all three directions in space. The changes in shape can be
either
continuous or abrupt, such as, for example, in the case of sharp-edged
structures, such
as edges, corners and/or points, which describe a defined angle which results
from two
or more planes meeting one another. Furthermore, "three-dimensional shaping"
is also
to be understood as meaning the complete surrounding or simultaneous
lamination of
fronts and edges, of regular or irregular moldings, profiles and the like.
Polyamide, polyimide, polyurethanes, polypropylene, polyethylene,
polyacrylonitrile,
polyvinyl alcohol or various polyesters, for example polyethylene
terephthalate,
polybutylene terephthalate, polytrimethylene terephthalate or polyethylene
naphthalate,
are advantageously used as starting material for the fibers of synthetic
polymers. The
use of fibers of polyamide, polyester, polypropylene or polyethylene is
preferred.
Mixtures of fibers of synthetic polymers are likewise advantageous. For
example, a
mixture of two of the abovementioned synthetic fibers, such as, for example,
polyamide, polypropylene, polyethylene and polyester fibers, in a weight ratio
of from
1:99 to 99:1, can be used. Depending on the specification of the decorative
papers to
be obtained, it is possible to choose advantageous fiber mixtures, it also
being possible
for more than two fiber types to be present.
It is also possible to use fibers of copolymers or polymer blends, for example
block
polymers or polymer blends of polyamide, polyimide, polyurethanes,
polypropylene,
polyethylene, polyacrylonitrile, polyvinyl alcohol or various polyesters, for
example
polyethylene terephthalate, polybutylene terephthalate, polytrimethylene
terephthalate
or polyethylene naphthalate, being used. Copolymers of monomers such as, for
axamnla nrnnvl?na Pthvlana (math)arrvlnnitrila vinvl alrnhnl nr actc?rc fnr
axarnnla nf
r -e r r~ - 1 - %i- j - V r -
vinyl alcohol, may also serve as a basis for the production of the synthetic
fibers.
The fibers of synthetic polymers are advantageously branched as little as
possible, in
particular unbranched. The individual fibers have lengths similar to those of
typical
natural fibers. Advantageously, the synthetic fibers have a length of from 0.5
to 20 mm,
in particular from 0.5 to 10 mm, particularly preferably from 2 to 10 mm. The
fiber
diameter is as a rule from 5 to 30 m, preferably from 10 to 25 m. The fibers
furthermore have a mean surface area of from 1500 to 3500 m2/g, in particular
from
2000 to 2500 m2/g.
The production of the synthetic fibers is known to a person skilled in the
art.
Conventional production processes are, for example, the spinning process or
production by means of the flashing process.
The synthetic fibers can be mixed in any desired ratio with the pulp fiber of
the
decorative paper comprising, for example, birch, eucalyptus and long-fiber
pulp, such
PF 55625 CA 02564692 2006-10-25
4
as pine or spruce, and can be processed on all conventional paper machines.
Furthermore, other tree species or gas, bush and cereal pulps are also
suitable.
Further details are to be found in "Fasern fur den Papiermacher" from P.
Keppler
Veriag KG. The pulps are obtainable, for example, by means of the sulfite or
of the
sulfate production process. The pulps can, if appropriate, be bleached by
various
methods known to a person skilled in the art. The cellulose fibers are
selected
according to the field of use, the advantages and disadvantages of the
individual
cellulose fibers being known to those skilled in the art. The processing of
the fibers to
give decorative paper is generally known. Depending on the fiber type and
fiber content
used, slight changes in the papermaking are required, for example in the fiber
mixing,
fiber pretreatment, fiber addition, beating and process control. During the
drying of the
decorative paper, the temperature should advantageously not exceed a range
from 50
to 150 C. Temperatures above 120 C can lead to reduced sheet thickness.
Furthermore, conventional finishing processes, such as, for example,
calendering,
adhesion, embossing, printing (for example gravure, flexography, digital
printing),
impregnation, molding and/or varnishing, can be effected downstream of the
generally
known decorative papermaking.
The decorative papers used according to the invention have a Bendtsen porosity
of
from 300 to 2000 mI/min, in particular from 400 to 1200 mi/min, and thus
possess very
good impregnatability. The porosity is appropriately adapted to the
impregnation
requirements. The wet strength is advantageously from 6 N to 40 N. The
covering
power of the decorative paper is as a rule from 0 to 100%, in particular from
60 to
100%. The decorative paper usually has a basis weight of from 40 to 300 g/mz,
in
particular from 80 to 200 g/m2. The perceived color is between white and
black, and
colors in numerous shades can he reali7eci.
The decorative papers may be smooth on one or both sides, smoothness on one
side
being preferred.
The decorative paper which comprises from 5 to 90% by weight, based on the
total
fiber content, of fibers of synthetic polymers advantageously comprises from
95 to 10%
by weight of cellulose. The cellulose is advantageously chemically unchanged.
The
cellulose can in principle be used in bleached or unbleached form. The use of
bleached
cellulose is preferred. Advantageously, eucalyptus globulus, Nordic birch and
long
fibers are used. The decorative paper preferably comprises from 10 to 60% by
weight,
based on the total fiber content, of fibers of synthetic polymers and from 90
to 40% by
weight of cellulose. In particular, the decorative paper comprises from 10 to
40% by
weight, based on the total fiber content, of fibers of synthetic polymers and
from 90 to
60% by weight of cellulose. Particularly preferably, the decorative paper
contains from
10 to 40% by weight, based on the total fiber content, of fibers of polyamide,
polyester,
polypropylene and/or polyethylene.
PF 55625 CA 02564692 2006-10-25
In addition to the cellulose fibers and the fibers of synthetic polymer, the
decorative
paper used according to the invention may comprise other conventional
components
known to a person skilled in'the art, such as, for example, secondary fibers,
fillers or
pigments. The inorganic or organic pigments control, inter alia, the opacity
production,
5 imparting of color, printability and increase in thickness. Advantageously,
white or
colored pigments as compounds in the form of oxides, silicates, carbonates,
sulfates or
carbon blacks may be present in the formulation.
Preferred inorganic pigments which can serve as colorants in the decorative
paper
used according to the invention are, for example, iron oxides, iron
cyanoferrates,
sodium aluminum silicates and/or titanium dioxides. The titanium dioxides are
prepared, for example, by the chloride or the sulfate process. Depending on
the field of
use, they may be modified, for example coated. The modification can be
effected by
means of various materials, for example with phosphorus, phosphorus pentoxide,
aluminum, zirconium, alumina and/or silica.
Preferred organic pigments which may serve as colorants in the decorative
paper used
according to the invention are, for example, those from the class consisting
of the
monoazo pigments (for example products which are derived from acetoacetyl
arylide
derivatives or from P-naphthol derivatives), laked monoazo dyes (e.g. laked
(3-oxynaphthoic acid dyes), disazo pigments, condensed disazo pigments,
isoindoline
derivatives, derivatives of naphthalene- or perylenetetracarboxylic acid,
anthraquinone
pigments, thioindigo derivatives, azomethine derivatives, quinacridones,
dioxazines,
pyrazoloquinazolones, phthalocyanine pigments or laked basic dyes (for example
laked
triarylmethane dyes).
The total pigment content in the finished base paper is advantageously from 0
to 40%
by weight, based on the total paper, in particular from 5 to 20% by weight.
With the use
of pigments, from 5 to 10% by weight of pigments based on silicates and up to
20% by
weight, preferably from 0 to 15% by weight, of titanium dioxides and iron
oxides are
used.
The decorative papers having high wet strength can as a rule usually be
processed
again without problems within known standard processes.
Suitable crosslinkable aminoplast resins are all resins known to a person
skilled in the
art, in particular melamine/urea/formaidehyde and melamine/formaidehyde resin
or
mixtures thereof. These resins may have been partly or completely etherified
with
alcohols, preferably C,- to C4-alcohols, in particular methanol. Etherified
and
unetherified melamine/urea/formaldehyde and melamine/formaldehyde resins or
mixtures thereof are preferably used, in particular etherified and/or
unetherified
PF 55625 CA 02564692 2006-10-25
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melamine/formaldehyde resins, particularly preferably unetherified melamine/-
formaldehyde resins.
Resin mixtures which comprise unetherified melamine/formaldehyde
condensate(s), if
appropriate etherified melamine/formaldehyde condensate(s) and polymer
dispersion(s) are particularly preferred.
Particularly suitable resin mixtures are those which comprise
(i) from 5 to 90% by weight, in particular from 20 to 80% by weight, of one or
more
unetherified melamine/formaidehyde condensates,
(ii) from 0 to 80% by weight, in particular from 0 to 50% by weight, of one or
more
etherified melamine/formaldehyde condensates and
(iii) from 10 to 95% by weight, in particular from 20 to 80% by weight, of one
or more
polymer dispersions.
The stated amounts of the components (i), (ii) and (iii) sum to 100% by weight
and are
based on the liquid resin mixture.
Assistants and additives may also be added to the melamine resin mixture, for
example
from 0.1 to 50% by weight, preferably from 0.2 to 30% by weight, in particular
from 0.5
to 20% by weight, of urea, caprolactam, phenoldiglycol, butanediol and/or
sucrose,
based on 100% by weight of the mixture (i) to (iii). Furthermore, they may
comprise
conventional additives, such as, for example, wetting agents, curing agents
and
catalysts.
In addition, the resin mixture may comprise one or more of the following
components in
a total amount of frorn 0 to 5% by weight, based on the resin mixture: anionic
surfactants (sodium, potassium and/or ammonium salts of fatty acid and
sulfonic acid;
alkali metal salts of C,z- to C16-alkylsulfates; ethoxylated, sulfated and/or
sulfonated
fatty alcohols; alkylphenols; sulfodicarboxylated esters; polyglycol ether
sulfates),
nonionic surfactants (ethoxylated fatty alcohols and alkylphenols having 2 to
150
ethylene oxide units per molecule), cationic surfactants (ammonium,
phosphonium
and/or sulfonium compounds having a hydrophobic structural element which
cmprises
at least one long aliphatic hydrocarbon chain), starch, polyethylene glycol
and/or
poly(vinyl alcohol).
The following may be stated specifically regarding the resin components:
Melamine/formaldehyde condensates are used as resin component (i). The
preparation
of the resin component (i) is generally known. First, for example, 1 mol of
melamine is
condensed with from 1.4 to 2 mol of formaldehyde at a pH of from 7 to 9 and at
temperatures of from 40 to 100 C, until the suitable degree of condensation is
reached.
Advantageously, the molar ratio of melamine to formaldehyde is from 1:1.15 to
1:1.9,
preferably from 1:1.4 to 1:1.6.
PF 55625 CA 02564692 2006-10-25
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In the resin component (ii), melamine/formaldehyde condensates are etherified
with C,-
to C4-alkanols, such as methanol, ethanol, propanol and/or butanol or glycols,
such as,
for example, ethylene glycol, diethylene glycol, propylene glycol and/or
dipropylene
glycol. Methanol and butanol are preferred. The preparation of the resin
component (ii)
is generally known. For example, from 20 to 30 mol of methanol are added to
the
melamine/formaldehyde condensate and etherification is effected at a pH of 1
to 5 and
temperatures of from 40 to 80 C. The condensation conditions depend on the
water
dilutability desired for the resin, which is at least 1:6. After the
condensation, the
melamine resins are freed from excess alcohol and formaldehyde by
distillation. Any
residual formaldehyde present is reacted on addition of urea at temperatures
from
room temperature to 90 C, preferably from 60 to 70 C. Advantageously, the
molar ratio
of melamine to formaldehyde to ether group is from 1:1.2:1 to 1:6:6,
preferably from
1:2.5:2 to 1:5:4.5.
Copolymer dispersions whose copolymers preferably comprise carboxyl, hydroxyl,
amido, glycidyl, carbonyl, N-methylol, N-alkoxymethyl, amino and/or hydrazo
groups
are used as resin component (iii). The abovementioned functional groups in the
copolymer are obtained in a conventional manner by incorporating, in the form
of
polymerized units, corresponding monomers which carry these functional groups.
The copolymers comprise the abovementioned functional groups in general in
amounts
such that they may comprise, incorporated in the form of polymerized units,
from 0.1 to
50% by weight, preferably from 0.3 to 20% by weight, based on the copolymer,
of
these monomers having functional groups.
Monomers suitable as main monomers of the comononiers having the
abovementioned
groups are the conventional olefinically unsaturated monomers copolymerizable
therewith, for example C,- to C12-alkyl esters of acrylic acid and methacrylic
acid,
preferably C,- to C8-alkyl esters, e.g. methyl acrylate, methyl methacrylate,
ethyl
acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl
acrylate, butyl
methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, lauryl
acrylate and lauryl
methacrylate; vinyl esters of C2- to C4-carboxylic acids, e.g. vinyl acetate
and vinyl
propionate, C,- to C4-dialkyl esters of maleic acid and fumaric acid,
vinylaromatics,
such as styrene, a-methylstyrene, vinyltoluene; acrylonitrile,
methacrylonitrile,
acrylamide, methacrylamide and vinyl ethers having 3 to 10 carbon atoms, vinyl
halides, such as vinyl chloride and vinylidene chloride; polyolefinically
unsaturated
compounds, such as butadiene and isoprene, and mixtures of the abovementioned
monomers, provided that they are copolymerizable with one another.
For the preparation of the resin mixture, the pH of the polymer dispersion is
usually
adjusted to 7.5 to 10 before the addition of the other components.
PF 55625 CA 02564692 2006-10-25
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The aminoplast resins thus obtained generally have solids contents of from 40
to 70%
by weight. Here, the solids content is defined as the dry residue which is
determined by
drying with 1 g of aqueous resin for two hours in a drying oven at 120 C. The
viscosity
of the aqueous resins is in the range from 10 to 200 mPa.s, preferably from 30
to 150
mPa.s (20 C).
The invention furthermore relates to aminoplast resin sheets or films
comprising
decorative papers which are impregnated with crosslinkable aminoplast resin
and
comprise from 5 to 90% by weight, based on the total fiber content, of fibers
of
synthetic polymers.
For the production thereof, the decorative paper described above and
comprising from
5 to 90% by weight, based on the total fiber content, of fibers of synthetic
polymers is
impregnated with the aminoplast resins in a manner known per se.
The aminoplast resins are used in the form of a 40 to 70 percent strength by
weight
aqueous solution, to which a curing agent is usually added.
Suitable curing agents are, for example, Bronstedt acids, such as organic
sulfonic
acids and carboxylic acids, and the anhydrides thereof, e.g. maleic acid,
maleic
anhydride and formic acid, ammonium compounds, e.g. ammonium sulfate, ammonium
sulfite, ammonium nitrate, ethanolammonium chloride and
dimethylethanolammonium
sulfite, and combinations of curing agents, such as morpholine/p-
toluenesulfonic acid.
The curing agents can be added in amounts of from 0 to 2.5% by weight, based
on the
aqueous impregnating resin. A person skilled in the art knows that the dose of
curing
agent can be adapted to the respective requirements for the application, it
being
possible appropriately to adjust the reactivity of the impregnating
resin/curing agent
mixtures, for example via the measurement of the turbidity times and gelling
times.
Assistants, such as wetting agents, may also be added to the impregnating
liquors.
Suitable wetting agents are, for example, ethoxylated fatty alcohols or
alkylphenol
ethoxylates, which can be added in amounts of from 0 to 1% by weight, based on
the
resin solution.
The manner in which the impregnating liquors are further processed to give
melamine
resin-impregnated products and the manner in which the wood-based materials
are
laminated with these impregnated products are known to a person skilled in the
art.
The decorative paper used can be processed to the same extent as for the
impregnation of known commercial decorative paper with aminoplast resins.
PF 55625 CA 02564692 2006-10-25
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The impregnation is effected as a rule in such a way that the decorative paper
is
thoroughly impregnated with the aminoplast resin solution. For example,
decorative
papers having a basis weight in the range from 60 to 200 g/mZ are impregnated
with
from 120 to 150% by weight, based on the paper weight, of the impregnating
liquor at
room temperature. The impregnated paper is then dried to a residual moisture
content
of from about 5 to 10% by weight. The conventional impregnating units which
introduce
the desired amount of resin onto and into the papers in the one-stage or two-
stage
process are suitable for the impregnation. The advantage of the two-stage
process is
that, if appropriate, different aminoplast resins can be used for the
preliminary
impregnation and subsequent impregnation.
The aminoplast sheets or films produced in this manner are then shaped in the
hot or
cold state. Advantageously the sheets or films are pressed with the substrate
at
elevated temperatures of, for example, from 150 to 210 C and/or elevated
pressures
of, for example, from 15 to 30 bar for a press time of, for example, from 10
to 60 s.
Advantageously, adhesion during lamination is effected by the aminoplast
resin, i.e.
self-adhesive aminoplast resin films are advantageously used for the 3D
shaping. In
some applications, however, the use of non-self-adhesive aminoplast resin
sheets can
also be advantageous; in this case, commercial adhesives or further adhesive
carriers
are used. Furthermore, subsequent adhesion may be advantageous in some
applications.
The substrate, in particular wood-base material or other molded carriers, such
as, for
example, premolded plastics or metal sheets, and the decorative paper can, for
example, be shaped together. This is advantageously effected by pressing in an
in-
mold press. However, a substrate having a three-dimensional structure and a
decorative paper of this contour or without a contour can also be shaped in a
corresponding manner. The three-dimensional shaping is advantageously effected
in a
membrane press or, if appropriate, in a press whose press plate corresponds to
the
negative shape of the three-dimensional carrier material.
For example, in such a membrane press, the upper and lower and/or lateral
sides of
the press mold consist of a membrane which can be subjected to pressure by
air,
nitrogen or liquid which, if appropriate, is heated (cf. WO 00/53667, on pages
16 to 18).
Advantageously, such a membrane press comprises a lower and an upper press
table,
a resilient membrane which can be pressed onto a substrate covered with
aminoplast
resin sheets or films and to be coated therewith and which, together with a
press table,
forms a pressure-tight chamber, channels for the inlet and outlet of a fluid
coming into
contact with the membrane, and a press control.
PF 55625 CA 02564692 2006-10-25
The term "membrane which can be pressed onto" is understood as meaning both
membranes which can be lowered and membranes which can be raised or pressed on
from the side.
5 A membrane press which has two storage containers for two differently
thermostated
fluids, which are provided with operating valves which can be opened and
closed by
the press control is advantageously used for its three-dimensional shaping.
Advantageously, the membrane press has the conveying apparatus for the fluids.
The
membrane press preferably has separate inlets and outlets for each fluid.
Because the press preferably has two storage containers which contain
differently
thermostated fluids which can come into contact with the membrane alternately
via
operating valves and a conveying apparatus, it is possible to realize a press
having a
heating mixture and cooling cycle, by means of which a workpiece can first be
heated
and then pressed when cooled without it being necessary to transport it from
one press
to another press, which simultaneously has the substantial advantage that the
workpiece remains fixed in the press so that the material to be laminated
cannot
become detached and the laminated workpiece cannot buckle or distort since it
remains fixed in the membrane press until a minimum temperature is reached.
Advantageously, each storage container has a compressed-air valve and a vent
valve.
The content of the storage containers can be subjected to variable pressure
depending
on the individual process steps. Advantageously, heating apparatuses or
cooling
apparatuses for the fluid are arranged in the storage containers and can also
be cycled
in the event of increased demand for heating or heat removal during pressing.
A preferably used fluid is a liquid, such as water or thermal oil, which have
a high heat
capacity, so that the required quantities of heat can be supplied and removed
by the
fluids alone without it being necessary to heat or cool the press tables
themselves.
Thus, even their surfaces facing the press space can be equipped with
insulation
material so that no heat losses occur via the press tables. It is furthermore
advantageous that the storage containers, which have compressed air and vent
valves,
can be subjected to pressure or reduced pressure as a function of the process
steps
which can be carried out using the membrane press, so that changing of the
liquids can
be carried out in an accelerated manner or the press pressure can be made
available
in an optimized manner at any desired level or on the workpieces as an
aminoplast
resin sheets or films.
The membrane press advantageously has, as a conveying apparatus for the
liquids
below the first membrane, a second resilient membrane which, via a second
frame,
forms a second pressure-tight chamber together with the first membrane, which
chamber can be supplied with an operating fluid through inlets or outlets,
depending on
PF 55625 CA 02564692 2006-10-25
11
the individual process steps. Particularly advantageous here is the use of air
as
operating fluid, by means of which, when the second chamber is subjected to
internal
pressure, the liquid present in the first chamber between press table and
membrane
can be forced back into the storage container. Such a conveying apparatus for
liquids
has minimum technical complexity and at the same time is extremely simple and
effective and requires little maintenance.
The membrane press described can furthermore advantageously be used for three-
dimensional shaping if flexible aminoplast resin sheets or films (cf. DE 103
01 901)
comprising absorptive cellulose-containing fibers, woven fabrics or decorative
papers
known from the prior art and impregnated with, for example, aminoplast resins
obtained
from unetherified melamine/formaldehyde condensate(s), if appropriate
etherified
melamine/formaldehyde condensate(s) and polymer dispersion(s), as described
further
above, as described, for example, in DE 200 19 180, are used.
The lamination is preferably effected over an extensive area in a single
operation.
Furniture parts whose mechanical stress is low are advantageously laminated
with a
single-ply decorative film. Particularly preferably, only a single decorative
paper is used
for the structure to be laminated.
Suitable substrates are particularly preferably wood-base materials, such as,
for
example, wood fibers or particle boards or MDF or HDF boards.
The aminoplast resin sheets or films according to the invention are
distinguished in
particular by the fact that surfaces which are resistant to cracking, glossy
and
insensitive to water vapor are obtained by pressing the aminoplast resin
sheets or films
onto substrates having a three-dimensionally structured surface of different
materials,
such as wood, plastics, fiber composites or in particular wood-base materials,
e.g.
plywood, wood fiber boards and in particular particle boards. Furthermore, the
aminoplast resin films according to the invention are particularly suitable
for completely
or partly surrounding moldings. In particular, the surfaces have a very
brilliant color.
Typical fields of use for the aminoplast resin sheets or films according to
the invention
are, as described above, furniture parts, such as, for example, kitchen
fronts, panels,
picture frames, door frames, doors, table tops, window sills, fronts or
accessories.
Examples
A) Production of the decorative paper 1
A paper was produced from a mixture of eucalyptus (20% by weight), birch (80%
by
weight), polyamide and polyester fibers (in each case 15% by weight, based on
the
pulp) in a Fourdrinier machine. Titanium dioxide (10% by weight, based on the
total
PF 55625 CA 02564692 2006-10-25
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fibers) and silicate (5% by weight, based on the total fibers) were added to
this fiber
mixture. The paper had a basis weight of 131 g/m2 and exhibited a Bendsten
porosity
of 990 mI/min.
131) Resin system 1
Component 1: A mixture of 730 g of 40% by weight aqueous formaldehyde and 334
g
of water was thermostated at 30 C. The pH of the mixture was adjusted to about
9.5
with 25% by weight of aqueous sodium hydroxide solution. 790 g of melamine
were
then added. The reaction mixture was then heated to 100 C, the pH decreasing
slowly.
Stirring was effected for about 60 min at a pH of from 8.6 to 8.8. As soon as
a sample
of the reaction mixture had a turbidity temperature of 50 C, the reaction
mixture was
cooled to room temperature.
Component 2: 8.4 g of sodium peroxodisulfate and 600 g of water were initially
taken in
a reaction vessel and heated to 80 C. While maintaining the temperature, feed
1 was
added continuously in the course of one hour. Feed 1 was prepared from 387 g
of
demineralized water, 151.2 g of 2-hydroxyethyl methacrylate and 58.8 g of
acrylic acid.
After the beginning of feed 1, feed 2 was added in the course of a further 45
minutes.
Feed 2 consisted of a solution of 81 g of demineralized water and 2.1 g of
sodium
peroxodisulfate. After the end of feed 1, the temperature was maintained for
one hour,
and feed 3 was then added at 80 C in the course of 1.5 hours and feed 4 in the
course
of 2 hours. Feed 3 consisted of an aqueous monomer emulsion comprising 410 g
of
demineralized water, 4.7 g of a 45% by weight aqueous solution of the surface-
active
substance corresponding to Dowfax 2A1, 378 g of styrene and 436.8 g of n-butyl
acrylate. Feed 4 consisted of a solution of 410 g of demineralized water and
10.5 g of
sodium peroxodisulfate. After the end of feed 4, the mixture was allowed to
react for
one hour at 80 C. Cooling to room temperature was then effected, 134.4 g of a
25% by
weight aqueous sodium hydroxide solution were added and filtration was
effected over
a 200 m sieve. The solids content of the dispersion obtained was 34.4% by
weight
and the pH was 7.1.
70% by weight of a solution consisting of component 1 were added to 30% by
weight of
a solution of component 2 while stirring. The resin mixture had a viscosity of
65 mPa.s
and a solids content of 51.2% by weight.
B2) Resin system 2
A mixture of 812 g of 40% by weight aqueous formaldehyde and 358 g of water
was
thermostated at 30 C. The pH of the mixture was adjusted to about 9 with 25%
by
weight of aqueous sodium hydroxide solution. 821 g of melamine were then
added.
Thereafter, heating to 100 C was effected and condensation was then carried
out to a
turbidity point of 50 C. After the turbidity point had been reached, the
reaction mixture
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was immediately cooled. A pH of about 9.2 was established with 25% by weight
aqueous sodium hydroxide solution. The resin solution has a viscosity of 45
mPa.s
(20 C).
C) Impregnation
Decorative paper from example 1 and standard decorative paper were impregnated
with the resin mixture from example 1 and the resin from example 2, after
addition of
about 0.5% by weight of curing agent (e.g. curing agent 529 liquid from BASF
AG), and
were dried, in such a way that, when fully impregnated, the decorative papers
had a
solids content of from 120 to 130% and possessed a residual moisture content
of from
6 to 10%.
D) 3D lamination
The melamine resin film obtained was pressed onto an MDF (medium density
fiber)
board having a diameter of 16.5 cm, comprising a 3D structure. 3D structures
are to be
understood as meaning contours having round and straight surfaces and/or edges
having a defined angle. The pressing process took place in a laboratory press
at from
150 to 160 C under a force of 45 kN and in a time of 30-60 s.
E) Characterization
El) Shapeability
The shapeability and the adhesion of the melamine resin film on the MDF board
comprising a 3D structure was assessed. In the case of good shapeability, the
lamination should rest completely against the structure and adhere firmly
thereto
without tearing, breaking or creasing.
Assessment:
0 = free of tears or creases
1 = free of tears, isolated creasing
2 = isolated tearing, slight creasing
3 = slight tearing, moderate creasing
4 = moderate tearing, pronounced creasing
5 = pronounced tearing, very pronounced creasing
6 = broken and destroyed surface
E2) Characterization of the surface
The melamine resin film obtained was pressed on to a smooth MDF board at 160-
165 C under a pressure of 2.5 N/mm2 and in a time of 110 s. The following
tests were _
carried out:
E2. 1) Curing
The quality of the curing was determined by the action for 16 hours of a 0.2N
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hydrochloric acid which is stained with 0.004% by weight of Rhodamine B
solution on
the smooth laminated MDF board. In the case of good curing, the surface is not
attacked by the acid. The strength of the attack can be assessed on the basis
of the
strength of the red coloration.
Assessment:
0 = no attack
1 = slight pink coloration
2 = substantial red coloration
3 = strong red coloration
4= strong red coloration with slight surface swelling
5 = strong red coloration with strong surface swelling
6 = destroyed surface
E2.2) Cohesiveness
The cohesiveness or porosity of the laminated surface serves for assessing the
sensitivity to dirt. Black shoe cream was rubbed into the surface to be tested
and said
surface was then cleaned again using a cloth. The shoe cream remaining in the
pores
permits an assessment of the cohesiveness of the surfaces.
The assessment of the surface cohesiveness is effected in the following steps:
0 = pore-free
1 = isolated pores
2 = few pores
3 = frequent pores
4 = many open areas
5= very many open areas
6 = no cohesivenesses
The results are presented in table 1.
Table 1
Experiment Paper Resin 3D surface Curing Cohesive-
system ness
1 Standard' 2 5 0 0
2 Standard' 1 3 1-2 1-2
3 Decorative 2 1-2 2-3 2-3
(according to paper 1
the invention)
4 Decorative 1 0 0-1 1
(according to paper 1
the invention)
'Commerical white decorative paper
